A fortnight after Diwali, on the day of Kartik poornima, a village on the confluence of rivers Ganga and Gandak in Bihar become the site of Asia's largest Cattle fair and attracts traders from as far as Central Asia. The Sonepur fair goes on for more than a fortnight. The fair is held to commemorate the event when Vishnu in the avatar of Harihar Nath came to the rescue of a devout elephant, Gaj Grah, who was attacked by a crocodile while the elephant was paying obeisance to him. Hence central to the fair is the temple of Harihar Nath, taking a holy dip in the rivers and ceremonial bathing of elephants.
The fair is also historically significant; Chandragupta Maurya is believed to have bought elephants for this army here. Apart from the elephants various breeds of dogs, donkeys, ponies, Persian horses, goats, bulls, buffaloes as well as a large variety of (sometimes illegal) birds can be seen at the fair.